But their late-morning liaison was captured on the CCTV, and staff were waiting for the pair when the train pulled into Wollongong Railway Station.

Staff reported finding a "large and disgusting" liquid mess on the floor, which they originally thought was urine, but Brennan explained it was Cola that he had used to clean himself up.

"I got a blow job on the train and I was rinsing my c**k off," he told officers, according to the Illawarra Mercury.

He later informed police he didn't have to "pay for it".

Shane Brennan, 38, said he couldn’t turn down the woman’s offer of oral sex on a train.

He toldthe Daily Mail he now regrets his actions after receiving a "bollocking" from a magistrate and having the encounter written up in the regional newspaper, and feared his partner may find out.

"As soon as the deed was done I was out of there and off ... I didn't know they had cameras all throughout the train."

The woman, who is known to police, confirmed Brennan's story.

Brennan said no one was in the carriage during the 9.56am service, and their tryst was over within minutes.

"How can you be so lucky and unlucky in the one day?" he asked. "You'd think the train guard would've said 'good on ya, mate.'"

He explained that he poured the bottle of Coke over his genitalia for hygiene reasons.

The woman was a little younger than him and "wasn't a good sort", he said. It is unclear whether she was penalised over their encounter, which Brennan believes is unfair.

"She was the one masturbating," he said. "If she didn't offer me nothing I wouldn't have f***ing done it."

He pleaded guilty to offensive behaviour and wilful and obscene exposure at Wollongong Local Court on Tuesday and was placed on a good behaviour bond. He said the magistrate "wasn't happy" with him, which was "understandable".

Brennan's lawyer described the incident as "opportunistic", noting that the encounter had only been witnessed by a few people, despite the time of day.

"The facts speak for themselves ... he took the opportunity that presented itself," the solicitor said.

Magistrate Mark Douglass convicted Brennan on both counts, saying such behaviour would not be tolerated.

"There's a line in relation to decency in our community and you have well and truly crossed it," he said.